Effect of Variations\nof Amine Content and Network\nBranching on Thermomechanical Properties of Epoxy Systems

In thermosetting epoxies, thermomechanical properties\ncan be enhanced\nby conscious selection of curing agents. Full cross-linking leads\nto a maximum in the glass- transition temperature. However, the relation\nbetween the glass transition temperature and the epoxy matrix depends\non several factors beyond the cross-linking degree, such as the molecular\nweight of the polymers, network organization, amount of branching,\nand the presence of hydrogen bonds. In this study, we investigated\nadding non- stoichiometric ratios of the epoxy resin Epikote 828 and\nthe curing agent Jeffamine D230. The investigations were done through\na combination of molecular dynamics simulations and experiments, primarily\ndifferential scanning calorimetry and nanoindentation. Reorganization\nof the network to fewer clusters with a higher degree of linearity\novercomes the effect of cross-linking and leads to a reduction of\nglass-transition temperature with increasing concentrations of curing\nagent to epoxy. The elastic, shear, and compressive moduli remained\nconstant. Hence, moderating the curing agent con- tent has the potential\nto improve thermal properties while maintaining mechanical properties\nfor this epoxy system.